Have you played 7th Dragon 2020? It's a psp game, and Miku Hatsune is there though she is not a main character. It's a great game(for me..)The graphics is cute cause they look like nendroid characters..
Plot: Year 2020, Dragons invaded the Tokyo and almost covered the cities with a flower called “Flowera”. The 13th squad (Your Party) from Murakumo Division is assigned to slay the dragons and save the civilians in every city. Game play: It’s an adventure type game, go on quests, kill dragons and etc. Its fighting style is like “What will Character A do? Attack | Defense | Skill | Item | Exhaust | Run”. By killing the Boss and Mid-Boss Dragons, you’ll earn a DZ which you need for the repair of the destroyed Murakumo Building, You need it to get more quest and for the story to move. Character Jobs: You can Choose whether it is a male or female, and Voice Actors such as Daisuke Ono[Shizuo’s VA] and Kamiya Hiroshi[Izaya’s VA]. Unfortunately, you can’t customize the characters looks and 3 members is the maximum number of person in a party. Samurai: Specializes in Close-combat, can switch sword to katana by some skill. Destroyer: Specializes in powerful attacks and anti-dragon skills. Hacker: Specializes in buffing skills[Atk up, def up…] Psychic: specializes in offensive and defensive magic. Trickster: Specializes in speed and agility. Can use Knife [close attacks] or Gun[ranged attacks].
Here's the video trailer: http://www.youtube.com/watch?v=zpKdFXwVmhk
Oh good, a PSP RPG! Seriously, why the hell are these not as dominant on this console when it's perfect for them? >.> This actually interests me a bit, though most RPGs are kind of hard to play in a language you aren't fluent in.